The invention relates in general to the drying and preheating of moist coal and the dry quenching of coke. More particularly, the invention relates to the combination of apparatus for dry quenching hot coke and to apparatus for the continuous drying and preheating of coal utilizing heat imparted by the glowing coke to the quenching gas, with a closed flow circuit for the quenching gas and with a flow path for drying gas passing through a drying and heating arrangement for the coal which is to be converted into coke.
An arrangement of this general type is disclosed in West German Offenlegungsschrift No. 2,304,541. The known arrangement continuously sucks in carburated gas to be employed as the drying gas. The gas is passed through a heat exchanger and brought to the required temperature by means of indirect heat exchange with the hot quenching gas and, after passage through the coal drier, freed of dust and then discharged. The drying gas must be an inert gas, i.e., in particular a gas which is low in oxygen, so as to avoid undesired reactions during the heating of the coal. Use is preferably made of nitrogen. However, the use of nitrogen is a quite expensive expedient. The fact that the quantity of gas to be freed of dust is very large leads to the incurrence of additional expense.
West German Offenlegungsschrift No. 2,304,541 additionally discloses a second arrangement of the general type in question. This second arrangement makes use of a single closed gas flow circuit passing through both the quenching bunker and through the coal drier. In this arrangement, the quenching gas also serves as the drying and heating medium for the starting material. Operation of such an arrangement is characterized by many practical disadvantages and difficulties. The circulating gas stream, containing substantially all the water vapor developed in the coal drier, enters the quenching bunker and upon contacting the hot coke in the quenching bunker forms water gas in considerable amounts. On the one hand, the water gas reaction results in a considerable furnace loss of the coke and, on the other hand, the highly explosive water gas creates very serious safety problems.
Another coal drying method of the general type in question is disclosed in West German Auslegeschrift No. 1,187,584. With this method, the heat generated during the quenching is not utilized for heating the drying gas. The drying gas travels through a flow path. A part of the gas, specifically as much as corresponds to the increase of the total gas quantity due to the addition of water vapors in the coal drier, is discharged into the free atmosphere. The drying gas, after a certain start-up period, becomes composed almost exclusively of superheated steam. With this method, avoiding condensation constitutes a serious problem, since such condensation creates the possibility of damage due to corrosion and during operation can lead to pressure fluctuations which are difficult to control.